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“Ambient Backscatter” Could Power Devices in the Future

University of Washington researchers believe we may be one step closer to an “Internet-of-things” reality. UW engineers have created a new wireless communication system that allows devices to interact with each other without relying on batteries or wires for power. Using something they call “ambient backscatter,” these devices can interact with users and communicate with each other without using batteries. They exchange information by reflecting or absorbing existing radio signals. The new communication technique takes advantage of radio frequency emissions that already surround us. Two devices communicate with each other by reflecting the existing signals to exchange information. The researchers built small, battery-free devices with antennas that can detect, harness and reflect a television signal, which then is picked up by other similar devices. The technology could enable a network of devices and sensors to communicate with no power source or human attention needed.

“We can repurpose wireless signals that are already around us into both a source of power and a communication medium,” said lead researcher Shyam Gollakota, a UW assistant professor of computer science and engineering. “It’s hopefully going to have applications in a number of areas including wearable computing, smart homes and self-sustaining sensor networks.”

“Our devices form a network out of thin air,” said co-author Joshua Smith, a UW associate professor of computer science and engineering and of electrical engineering. “You can reflect these signals slightly to create a Morse code of communication between battery-free devices.”

Everyday objects could be enabled with battery-free tags to communicate with each other. For instance, a couch could use ambient backscatter to alert someone who had been sitting there where the user’s keys were left. Smart sensors could be built and placed permanently inside nearly any structure, then set to communicate with each other. For example, sensors placed in a bridge could monitor the health of the concrete and steel, then send an alert if a sensor picks up a hairline crack. The technology can also be used for communication — text messages and e-mails, for example — in wearable devices, without requiring battery consumption.

Researchers demonstrated how one payment card could transfer funds to another card by leveraging the wireless signals surrounding them. Ambient RF provides both power source and communication medium.

The researchers tested the ambient backscatter technique with credit card-sized prototype devices placed within several feet of each other. For each device the researchers built antennas into ordinary circuit boards that flash an LED when receiving a signal from another device. Groups of the devices were tested in a variety of settings in the Seattle area, including inside an apartment building, on a street corner and on the top level of a parking garage. These locations ranged from less than one-half away from a TV tower to about 6.5 miles away.

They found that the devices — even the ones farthest from a TV tower — were able to communicate with each other. The receiving devices picked up a signal from their transmitting counterparts at a rate of 1 kilobit per second when up to 2.5 feet apart outdoors and 1.5 feet apart indoors. This is enough to send such information as a sensor reading, text message or contact information.

It’s also feasible to build this technology into devices that do rely on batteries, such as Smartphones; when the battery dies, the phone could still send text messages by expropriating power from ambient RF. The researchers says applications are endless, and they plan to continue advancing the capacity and range of the ambient backscatter communication network.

The research was funded by the University of Washington through a Google Faculty Research Award and by the National Science Foundation’s Research Center for Sensorimotor Neural Engineering at the UW. The originalarticle and video are on the UW website. For more information, contact Gollakota and Smith at abc@cs.washington.edu. — The University of Washington